Increase strictness when using applyVariant on illegale candidates (#9599)

* ensure that cases like `@-[200px]` and `group[:hover]` aren't allowed

* update changelog

CHANGELOG.md

@@ -58,6 +58,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Don't require `content` key in custom plugin configs ([#9502](https://github.com/tailwindlabs/tailwindcss/pull/9502), [#9545](https://github.com/tailwindlabs/tailwindcss/pull/9545))
 - Fix content path detection on Windows ([#9569](https://github.com/tailwindlabs/tailwindcss/pull/9569))
 - Ensure `--content` is used in the CLI when passed ([#9587](https://github.com/tailwindlabs/tailwindcss/pull/9587))
+- Increase strictness when using `applyVariant` on illegale candidates ([#9599](https://github.com/tailwindlabs/tailwindcss/pull/9599))
 
 ## [3.1.8] - 2022-08-05
 

src/lib/generateRules.js

@@ -162,10 +162,23 @@ function applyVariant(variant, matches, context) {
 
   // Retrieve "arbitrary value"
   if (variant.endsWith(']') && !variant.startsWith('[')) {
-    let match = /-?\[(.*)\]/g.exec(variant)
+    // We either have:
+    //   @[200px]
+    //   group-[:hover]
+    //
+    // But we don't want:
+    //   @-[200px]        (`-` is incorrect)
+    //   group[:hover]    (`-` is missing)
+    let match = /(.)(-?)\[(.*)\]/g.exec(variant)
     if (match) {
-      variant = variant.replace(match[0], '')
-      args.value = match[1]
+      let [, char, seperator, value] = match
+      // @-[200px] case
+      if (char === '@' && seperator === '-') return []
+      // group[:hover] case
+      if (char !== '@' && seperator === '') return []
+
+      variant = variant.replace(`${seperator}[${value}]`, '')
+      args.value = value
     }
   }
 

tests/generate-rules.test.js

@@ -0,0 +1,47 @@
+import { css } from './util/run'
+
+import { generateRules } from '../src/lib/generateRules'
+import resolveConfig from '../src/public/resolve-config'
+import { createContext } from '../src/lib/setupContextUtils'
+
+it('should not generate rules that are incorrect', () => {
+  let config = {
+    plugins: [
+      ({ matchVariant }) => {
+        matchVariant('@', (value) => `@container (min-width: ${value})`)
+      },
+    ],
+  }
+  let context = createContext(resolveConfig(config))
+  let rules = generateRules(
+    new Set([
+      // Invalid, missing `-`
+      'group[:hover]:underline',
+
+      // Invalid, `-` should not be there
+      '@-[200px]:underline',
+
+      // Valid
+      'group-[:hover]:underline',
+      '@[200px]:underline',
+    ]),
+    context
+  )
+
+  // Ensure we only have 2 valid rules
+  expect(rules).toHaveLength(2)
+
+  // Ensure we have the correct values
+  expect(rules[0][1].toString()).toMatchFormattedCss(css`
+    .group:hover .group-\[\:hover\]\:underline {
+      text-decoration-line: underline;
+    }
+  `)
+  expect(rules[1][1].toString()).toMatchFormattedCss(css`
+    @container (min-width: 200px) {
+      .\@\[200px\]\:underline {
+        text-decoration-line: underline;
+      }
+    }
+  `)
+})